how tether works at an abstract level is like this. I'm tether and I issue an instrument called USDT, which I announce is pegged to the dollar at par. in order to support this peg I back USDT one-for-one with dollars and only issue new ones when someone buys them for dollars. eventually I realise that having a big pile of cash sitting around doing nothing isn't actually profitable business model, so I decide to buy some high-grade liquid debt with it. then I realise that all of my assets don't need to be highly liquid, bc the prospect of all my customers asking for their money back at the same time is very unlikely. so I can move some of my portfolio into longer term, less liquid and maybe more speculative stuff (crypto, for example) with a higher yield, but keep enough lliquid assets to meet the cashflow demands of my depositors. then it occurs to me that I don't need to wait for dollars to come in to buy the speculative assets, if those assets are crypto, since I can pay for them with USDT. So I can expand my balance sheet at will, issuing new tethers and using them to by existing crypto assets. finally, I realise that I don't need to wait for existing assets to come about, I can simply make loans of USDT to trusted counterparties and create the assets myself. if the price of USDT falls, I just sell some of my assets for USDT, pushing the price back up. ta-da, I've become the bank of tether, the central bank of the crypto economy.